Prognosis for myalgic encephalomyelitis and chronic fatigue syndrome

From MEpedia, a crowd-sourced encyclopedia of ME and CFS science and history

Prognosis refers to the expected course of a disease and the prospect of recovery.[1][2] According to the most recent review, the prognosis for myalgic encephalomyelitis and chronic fatigue syndrome (ME and CFS) is considered to be fairly poor, with only a small minority (a median average of 5%) fully recovering (returning to pre-morbid levels of functioning).[3][4] The majority of patients - 95% - remain ill with significantly impaired functioning, however an estimated 40% of ME/CFS patients do achieve substantial improvements despite not fully recovering.[3][5] and the prognosis in adolescents is considered to be better than in adults.[6][7]

Due to heterogeneity in methodology, such as case definition, length of follow-up and assessment of recovery, the estimated prognosis of ME/CFS is variable and uncertain.[6] According to ME expert Charles Shepherd, “there is a wide spectrum of severity, variability and degrees of improvement and deterioration in ME/CFS – and so prognosis can very difficult to predict with any certainty in an individual case."[8]

Recovery rates[edit | edit source]

Follow-up studies[edit | edit source]

In one of the first extensive studies on the prognosis of ME/CFS, Peterson et al. studied 65 patients who fulfilled the Holmes criteria after a one-year follow up. Though 40% reported improvement, none of the patients considered themselves recovered.[9] Similar results were reported by an Australian team in 1994. They followed up on 103 patients for a mean of 3.2 years. Although the majority reported improvement, less than 6% had completely recovered.[10] Two years later, a Dutch research team from Nijmegen published results for their large sample of 246 ME/CFS patients. After a 1.5 year follow-up only 3% said they had recovered and only 17% reported improvement.[11] One of the first reports on prognosis using the Fukuda criteria was published by Saltzstein et al. Because they studied ME/CFS patients in primary care, recovery rates were generally higher, around 20%.[12] In 2017, Collin & Crawley studied the prognosis of 418 ME/CFS patients who had been treated in a British ME/CFS centre and diagnosed according to the NICE criteria. Two and a half years later less than 6% said they no longer suffered from ME/CFS and 30% reported their health had deteriorated.[13] All of the aforementioned studies used different diagnostic criteria – the Holmes, Australian,[14] Oxford, Fukuda and NICE criteria respectively – but reported similar poor outcomes, with only a tiny minority of ME/CFS reaching full recovery. 

Community-based studies[edit | edit source]

The poor prognosis observed in tertiary and primary care was confirmed by the epidemiological study in Chicago. Of the 32 ME/CFS patients identified in the late 1990s, 24 were evaluated after a period of approximately 10 years. Of these, two thirds continued to have ME/CFS, 21% had developed exclusionary illnesses, 8% was now labeled as suffering of idiopathic chronic fatigue and only 4% had remitted.[15]

Work-related outcomes and objective measures[edit | edit source]

Although research has generally used self-reported improvement to estimate prognosis, some studies included more objective measurements such as work-related outcomes. These have generally reported less improvement. Vercoulen et al.[11] and Hill et al.[16] for example found no significant change in employment status. Another study from the research team of Benjamin Natelson found that unemployment rates increased after 3.5 year follow-up.[17] A Danish study followed up on 33 patients for an extensive period of 5 years. Though work disability was already high at baseline (77%), this increased even further to 91%.[18] A trend towards a decrease in employment status was also reported by Collin & Crawley, as more patients reported a deterioration than an improvement in hours spent on work, education and social activities[13] (see table below). 

Collin & Crawley 2017.
  return to work or increase their working hours increased their hours of, education increased unpaid work and domestic tasks increased their social and leisure activities
Improvement 24% 12% 36% 35%
Decline -27% -13% -32% -39%

Other studies have shown that ME/CFS patients do experience improvement on objective measures. Tiersky et al. (2002) for example noted better results on neurocognitive testing after a period of 3.5 years.[17] Rowe et al. reported a significant improvement in range of motion (ROM) in 53 adolescents with ME/CFS after a two year follow-up.[19]

The CDC's historically optimistic prognosis[edit | edit source]

Despite heterogeneity in diagnostic criteria and patient sample, most research is in agreement on the poor prognosis in ME/CFS (see table below). Research by the Centers for Disease Control and Prevention (CDC) however has controversially reported much higher recovery rates. In 1999, for example, the CDC surveillance system reported a “cumulative probability of recovery” from ME/CFS of 31.4% during the first 5 years of illness and 48.1% during the first 10 years of illness.[20] Data published in 2003 from the epidemiological research in Wichita, Kansas indicated even higher recovery rates. At the three year follow-up almost 80% no longer fulfilled the diagnostic criteria for ME/CFS, though a large minority (23.1%) were diagnosed with other diseases such as sleep disorders. More than half of the studied ME/CFS patients had experienced partial to total remission during follow-up.[21]

However, it should be noted that ME/CFS recovery definitions are inherently based on opinions rather than scientific measures, and influenced by factors like the diagnostic criteria used, etiological perceptions of ME/CFS, age and lifestyle status of patients, and misdiagnosis.[4]

Study Time period Number of patients Recovery rate Improvement (excludes recovery) Deterioriation
Peterson et al., 1991.[9] 1 year 65 (Holmes criteria) 0% About 40%  
Tirelli et al., 1994.[22] 2 years 265 (Holmes criteria) 3% 8.3%  
Wilson et al., 1994.[10] 3.2 years 103 (Australian criteria) 5.8% 63%  
Bombardier et al., 1995.[23] 1.5 years 226 (Holmes criteria) “Of the 226 patients who initially met CFS criteria, 103 (46%) continued to meet symptom criteria for CFS at follow-up”
Vercoulen et al., 1996.[11] 1.5 years 246 (Oxford criteria) 3% 17% 20%
Ray et al., 1997.[24] 1 year 136 (Oxford definition + PEM, sick less than 6 years) / 64.4% 14.8%
Saltzstein et al., 1998.[12] 2 years 15 (Fukuda criteria) 20% 40%  
Reyes et al., 1999.[20] 5/10 years 155 (Fukuda criteria) 31.4%/ 48.1%    
Pheley et al., 1999.[25] ? 177 (Fukuda criteria) 12%
Hill et al., 1999.[16] 1.8 years 23 (Holmes and Fukuda criteria) 4% 39%  
Van der Werf et al., 2002.[26] 1 year 78 (Fukuda CFS or idiopathic fatigue) 8% 38% 17%
Tiersky et al., 2002.[17] 3.5 years 35 (Holmes and Fukuda criteria)   57%  
Nisenbaum et al., 2003.[21] 1-3 years 24-65 (Fukuda criteria) Of the 50 patients who never developed a permanent exclusion, 62% experience a partial or total remission.
Andersen et al., 2004.[18] 5 years 33 (Holmes and Fukuda criteria)   15% 42%
Ciccone et al., 2010.[27] 0.5-2.5 years 92 (Fukuda criteria)   67%  
Jason et al., 2011.[15] 10 years 24 (Fukuda criteria) 67% still had CFS, 21% had developed exclusionary illnesses, 8% had Idiopathic chronic fatigue and 4% remitted
Nyland et al., 2014.[28] 6.5 years 92 (Fukuda criteria post-EBV) 13% 57% 12%
Collin & Crawley, 2017.[13] 1/ 2-5 years 418/385 (NICE guideline-criteria) 3%/6% said they no longer suffered from CFS/ME 28%/30.4% 8%/17%

The CDC information webpage has been criticized by patient organizations for painting the prognosis of ME/CFS in a positive light and overemphasizing natural recovery of the disease.[29] ME Action, for example, wrote:

“While presenting a more positive outlook may decrease physician discomfort in dealing with a chronic and debilitating disease like ME, it is disingenuous to imply that patients will return to good health when so few do. Moreover, this can delay patients from getting the social support they need to cope with a lifelong illness.”[30] 

Outbreaks[edit | edit source]

Longitudinal studies on ME outbreaks show that in its epidemic form, the disease tends to have a better prognosis. This might be because less strict diagnostic criteria were used in these studies or because patients were followed-up much earlier in their disease process (bypassing the normal six month waiting period). Levine et al. provided follow-up data from the outbreaks in the Nevada-California region (Incline Village, Truckee, Yerington and Placerville) during the 1980s. Twenty-nine patients were revaluated after a period of three years. Almost all subjects were able to return to pre-illness activity and the authors concluded that the overall prognosis was generally favorable.

“Among the patients we observed were a marathon runner, a marathon bicyclist, avid skiers, mountain climbers, and other individuals pursuing an unusually physically active life-style prior to their acute illness. All of these patients attempted to continue their activities and most of them, after periods ranging from 6 to 18 months, eventually were able to resume their previous activities.”[31]

Another follow-up study however, concluded that only an estimated 41% of patients during these outbreaks would fulfill the Holmes criteria of ME/CFS. The recovery rate for these ME/CFS patients was only 15%, much lower than the 30% for all patients of the Lake Tahoe outbreak.[32]

A 10 year follow-up of the outbreak at West Otago, New Zealand also reported a good prognosis. Though some needed to adapt their lifestyle to prevent relapses, most patients returned to premorbid activity.[33]

Follow-up data is also available for the outbreak in Akureyri, Iceland. Sigurdsson & Gudmundsson reported in 1955 that 13% of the patients he evaluated considered themselves completely recovered.[34] In 1988, Byron Hyde reported about 10 Icelandic ME patients in the Lancet, 40 years after the initial outbreak. Two of them (20%) indicated a “total physical and intellectual recovery”.[35]

Pediatric[edit | edit source]

Prognosis for adolescents with ME/CFS is generally considered to be more favorable than in adults.[36][37][38] Gill et al. reported that 4.5 years after an initial evaluation almost a quarter of adolescent ME/CFS patients reached “near to complete improvement”.[39] The diagnosis in this study however was made retrospectively (by looking at old charts and test results instead of a clinician’s assessment). A Dutch team followed up on 54 adolescents with ME/CFS. After an average of 2.2 years almost half of the sample said they've had almost completely recovered.[40]  David Bell followed up on 35 ME/CFS patients who fell ill during the Lyndonville outbreak in the 1980s. Prognosis was favorable: 37% said they had "recovered completely" and felt "entirely well.” A further 42.9% agreed with the statement “I have never recovered completely but feel pretty well."[41] Other studies (Rangel et al.,[42] Sulheim et al.,[43], Rimes et al.[44]) have reported similar high improvement/recovery rates in pediatric ME/CFS, though these studies did not use generally accepted diagnostic criteria of ME/CFS. In the Bulletin of the IACFS/ME Katherine Rowe claimed to have data for 256 young ME/CFS patients 12 years after initial evaluation. Eighty-eight percent reported recovery, though this information has not been reported in a peer-review publication.[45] In its 2015 report (p.183, 213), the National Academy of Medicine noted a lack of well-designed longitudinal studies on the prognosis of ME/CFS in children and adolescents.[46]

Dr. Bell notes that if an adolescent spent three months in bed due to ME/CFS they will still be ill at age 35 even if their symptoms were mild in their adult years. Becoming increasingly ill with activity and symptom severity is expected 15-20 years later.[47]

One study of young adults followed for fifteen years demonstrated clear improvement in activity, but not illness resolution8. The same group of patients continued to do relatively well for a further five to ten years and then became worse in both activity limitation and symptom severity12. It is rare for an adolescent to become completely free of the disease13.[47]

Children are diagnosed with ME/CFS at three months of illness under the Systemic Exertion Intolerance Disease (SEID) and Canadian Consensus Criteria (CCC) and myalgic encephalomyelitis (ME) is diagnosed immediately under the International Consensus Criteria (ICC).[48][49][50][51]

Treatment studies[edit | edit source]

Predictors of outcome[edit | edit source]

Several studies have looked at factors that influence the prognosis of ME/CFS, though results have generally been conflicting.

Age[edit | edit source]

Although some studies have found the age of adult ME/CFS patients to be associated with poorer outcomes (with older people having a worse prognosis), most studies did not find this correlation (see table below).  

Does age impact prognosis?
Yes No
Jason et al., 2011.[15] Bombardier et al., 1995.[23]
Tiersky et al., 2002.[17] Vercoulen et al., 1996.[11]
Pheley et al., 1999.[25]
  Reyes et al., 1999.[20]
  Ciccone et al., 2010.[27]

Matthews & Komaroff were able to follow-up on 92 ME/CFS patients for a long period of nine years. The authors noted that “physical function tended to improve for many patients over time, despite the fact that they were aging.” This suggests age is not a predictor of poor outcomes in adult ME/CFS patients.[52] Kidd et al. segmented ME/CFS patients into two groups: those younger and those older than 55. A comparison showed few meaningful differences. But when limited to those patients who had been sick for a long time, younger patients did have more autonomic and immune-related symptoms.[53]

Illness duration[edit | edit source]

Although many physicians believe that patients would benefit from earlier diagnosis and treatment, evidence for this is currently lacking.[54] Studies have generally been inconsistent regarding the duration of illness as a predictor of outcome. (see table below). 

Does duration of illness impact prognosis?
Yes No
Vercoulen et al., 1996.[11] Wilson et al., 1994.[10]
Ray et al., 1997.[24] Bombardier et al., 1995.[23]
Reyes et al., 1999.[20] Pheley et al., 1999.[25]
Nisenbaum et al., 2003.[21] Hill et al., 1999.[16]
Nyland et al., 2014.[28] Anderson et al., 2004.[18]

The CDC information website has been criticized for suggesting early intervention leads to better outcomes. In a detailed critique Jaime Seltzer from #MEAction wrote:

"Anyone who has gone undiagnosed for years or even decades understands that an accurate diagnosis and useful management strategies — such as avoiding overactivity and providing symptomatic relief — can improve quality of life. But there is no evidence that early intervention affects the likelihood of full recovery. When the CDC has been so cautious regarding what it recommends as treatment, this assertion, which is insupportable with current evidence, stands out."[29]

Friedberg et al. compared ME/CFS patients with a median length of illness of 18 years compared to a group of ME/CFS-patients who had been ill for less than three years.  Few differences existed between the two groups; although those with long illness duration had more cognitive difficulties (they also reported more sexual problems).[55] In a study by [Santamarina-Perez et al. (2011), no association was found between illness duration and neuropsychological test results.[56] Hornig et al. did find a distinct an increase in cytokine expression in the plasma of ME/CFS patients with illness duration less than three years, an increase that was not present in patients with longer illness duration.[57]

Illness severity[edit | edit source]

Many studies have found that illness severity at baseline is associated poorer outcomes over time. Disagreement exists however on which measures of illness best predict a worse prognosis.  While Pheley et al. (1999)[25] found an association with fatigue, Ray et al. (1997)[24] reported the broader concept of somatic symptoms to be associated with poor outcomes. In a Norwegian study that followed ME/CFS patients who got sick after mononucleosis, joint pain was an important predictor of prognosis.[28]

Does illness severity impact prognosis?
Yes No
Ray et al., 1997.[24] (somatic symptoms) Anderson et al., 2004.[18]
Pheley et al., 1999.[25] (fatigue)
Van der Werf et al., 2002.[26]
Jason et al., 2011.[15]
Nyland et al., 2014.[28] (arthralgia)
Ciccone et al., 2010.[27]

Psychiatric comorbidity[edit | edit source]

Though some studies have reported it, no convincing evidence exists that a comorbid psychiatric diagnosis worsens the prognosis of ME/CFS. One well-controlled study (Tiersky et al. 2002) even found an inverse relationship; patients with a concurrent psychiatric history showed more improvement over time.[17] The authors attributed this to varied presentations of symptoms in patients meeting the Fukuda criteria, which allows some patients with an underlying psychiatric etiology to be diagnosed with ME/CFS.

Does a psychiatric diagnosis impact prognosis?
Yes No
Bombardier et al.,1995.[23] (Dysthymia) Vercoulen et al., 1996.[11]
Pheley et al., 1999.[25] Ray et al., 1997.[24]
Nyland et al., 2014. (Depression)[28] Hill et al. (1999)[16]
  Tiersky et al., 2002.[17] (inverse relationship)

Infectious onset[edit | edit source]

A Japanese study indicated that the prognosis of postinfectious ME/CFS patients is better than in ME/CFS patients without an infectious onset.[58] Though the sample size was small, results were in line with other studies. A Norwegian team for example followed up on ME/CFS patients who had developed ME/CFS after infectious mononucleosis. After 6.5 years a large increase in employment status was seen.[28]

Sudden/gradual onset[edit | edit source]

DeLuca et al. (1997) compared patients with a sudden and gradual onset and found relatively few differences, except that the gradual onset group had more psychiatric comorbidity.[59] Two studies (Reyes et al. 1999[20]; Hill et al. 1999[16]) found that the type of illness onset was not a significant predictor of prognosis in ME/CFS. 

Comorbid fibromyalgia[edit | edit source]

Ciccone et al. reported that ME/CFS patients with comorbid fibromyalgia have a worse prognosis than ME/CFS patients without fibromyalgia.[27] Other studies had already shown that patients with both diseases are more physically impaired than patients who only have ME/CFS.[60][61]

Being diagnosed with CFS[edit | edit source]

In the community-study in Wichita, Kansas, researchers[21] were able to compare the prognosis of ME/CFS patients who were diagnosed versus those than weren't. Gijs Bleijenberg summarized the results as follows: 

"Remission was also not associated with the report of being ever diagnosed as CFS. Although the number of CFS diagnosed subjects was very low, it may mean that the diagnosis of CFS cannot be seen as unfavourable for remission. This is contrary the idea of some family doctors who are reluctant to diagnose their patients as having CFS, as they are afraid that this will facilitate an unfavourable course of the condition."[62]

Bell et al. (2001) were able to dispel another myth, namely the idea that ME/CFS symptoms persist because of encouragement by sympathetic physicians who might reinforce illness beliefs. In their 13-year follow-up study, the longest to date in ME/CFS, clinical empathy was not a prognostic factor.[41]

ME worse prognosis than CFS?[edit | edit source]

Hamilton et al. (2005) were able to probe the data of 18,000 patients who had been diagnosed by primary care physicians with either CFS, ME, fibromyalgia or postviral fatigue syndrome (PVFS). To estimate prognosis they looked at the percentage of patients who retained the label of any of these "fatiguing illnesses" at follow-up. Patients with ME were found to have a worse prognosis than patients with CFS, fibromyalgia or PVFS.[63]

Sex[edit | edit source]

Most studies have not found gender to be a significant predictor of prognosis (more references needed).[64][citation needed] Matthews & Komaroff (2007) did find women to have consistent higher physical function than men.[52]

‘Recovered’ but with lingering symptoms[edit | edit source]

In one of the most influential studies on the prognosis in ME/CFS, David Bell followed-up on the adolescents who fell ill during the Lyndonville outbreak in the 1980s. After a period of 13 years, more than a third of the sample considered themselves recovered.[41]  Yet when researchers looked at the symptoms these ‘recovered’ patients reported, they seemed to be much more disabled than healthy controls.[65] As Bell explains: 

“Some of the young adults rated their health as ‘good’, while the amount of activity they could perform was minimal. They had become so used to their performance level, they accepted it as their new normal. Unfortunately, many of them, while they described their health as good, they were unable to work full time or carry on other duties.”[66]

This suggested that 'recovered' ME/CFS patients did not reach their premorbid health, but have simply adjusted to ongoing somatic symptoms. Similar findings were reported by Reyes et al., who noted that "all patients, including those who reported recovery, stated that they continued to have some CFS-defining symptoms".[20]  Sankey et al. noted that the improvement patients reported "contrasts greatly with the numbers of symptoms that they were still experiencing when specifically asked. […] although 21 (75%) regarded themselves as fully recovered, they described symptom persistence of fatigue and headache, depression and sleep disturbance."[67] Another aspect that might have led to an overestimation of recovery in ME/CFS is the fluctuating nature of the disease. Anderson et al. (2004) for example noted: 

"Almost all our patients reported symptom fluctuation, including daily, weekly or monthly periods. This, together with our other findings, suggests that symptoms often improve or worsen without altering the overall severity of the illness."[18]

This is a confirmed by a study where ME/CFS symptoms were recovered at three time points in time. Hill et al. found that among patients who reported improvement at time two, about half were worse again at time three.[16]

Finally Adamowicz et al. (2014) noted that ME/CFS studies often use a limited assessment of recovery, for example by simple asking patients if they recovered or by looking at only one measure to assess improvement.[68] This might also have led to an overestimation of recovery in ME/CFS, as patients can improve on one measure and worsen on another. This was seen in a Norwegian study that used multiple measures of recovery. While the total sleep and rest time decreased, work disability increased. While attention during reading worsened, difficulty in driving a car improved.[18]  Adamowicz et al. pleaded for a multidimensional assessment of recovery that captures a broad-based return to health. Twisk argued that objective measures such as a cardiopulmonary exercise test, a tilt table test or neurocognitive tests, should be used to assess recovery.[69] Qualitative studies with physician experts and patients with ME/CFS show support for a multidimensional assessment of recovery, which would incorporate measurements of daily functioning, symptomatology, quality of life, and physical functioning.[70][71]

The course of ME/CFS[edit | edit source]

Disease onset[edit | edit source]

The disease ME/CFS often occurs when a person does not recover from a flu-like illness, EBV, mononucleosis, HHV, Q fever, another virus or other infections. Patients must meet one or more diagnostic criteria that define either myalgic encephalomyelitis (ME), chronic fatigue syndrome (CFS) or ME/CFS.[72][73] "Occasionally, ME/CFS has been triggered by environmental toxins, the receipt of an immunizing injection, or surviving a major physical trauma."[74]

Fluctuation[edit | edit source]

For most ME/CFS patients, their health is never the same and they experience numerous symptoms and disease severity which fluctuate day to day and through the years.[75][76][77] In multiple sclerosis, the clinical course of the disease can be divided into different subtypes as some patients experience a progressive decline, while others a more relapsing course with ups and downs.[78] Stroothoff et al. tried to make a similar subdivision in ME/CFS. Their analysis showed that the majority of ME/CFS patients describe their illness as fluctuating, with a minority (15.9%) said they were constantly getting worse.[79] Howes & Goudsmit had previously reported on a subtype of ME that progressively worsens over time.[80]

Fennell's 4 stages[edit | edit source]

Others have subdivided the course of ME/CFS into different stages. For example, in the 1990s, Patricia Fennell suggested four distinct stages.[81]

The first phase is about the process of getting sick, giving up hobbies or work, and looking for an explanation of symptoms.
In the second phase, the diagnosis has provided a kind of relief, while the disease usually stabilizes.
In the third phase, patients understand that they will not recover quickly and that their disease is chronic. At this stage patients go through a mourning process as they realize that their old self is gone and they have to adapt to a new identity. Although the illness is stable, they still experience relapses.
In the fourth phase, the patients reintegrate with their new identity; they set new goals and value a new way of living. Some experience improvement.

Jason et al. tested this model in 65 ME/CFS patients. Though analysis showed a three-factor solution that corresponded with Fennell's stages, almost none of the patients were in the fourth stage.[82] This was probably because participants were selected in a clinic and were still actively seeking health care. The analysis also showed that patients experiencing the first phase, the crisis phase, were sick for a longer time than patients in other stages. This suggests Fennell's subdivisions should not be seen as a linear development in time, but rather the progression patients make in dealing with illness and disability. 

Bell’s 3 stages[edit | edit source]

Based on the experience of adolescents he followed up for many years, David Bell subdivides the course of ME/CFS into three stages.[66] At the first stage, there is an acute illness where EBV is likely responsible for most adolescents but there is no standard viral illness. The initial virus likely fades away in a week and the patient feels better and is ready for regular activities. Bell adds "in a person with a gradual onset of symptoms, this stage would be different." The second stage "occurs when the symptoms do not disappear, but persist for months to years in roughly the same severity. There is little variation day-to-day, and this time is very confusing. Many medical providers are contacted, most giving conflicting opinions varying from psychological disorders to possible exotic infections, but the tests come back normal." In the third stage, patients will have mild, gradual improvements over years and patients adjust their lives to the symptoms. Patients may look well and recovery is thought to have taken place, but they still have to adapt their lifestyle to avoid relapses and symptom exacerbation.

See also[edit | edit source]

Learn more[edit | edit source]

References[edit | edit source]

  1. ↑ "PROGNOSIS | meaning in the Cambridge English Dictionary". dictionary.cambridge.org. Retrieved October 28, 2018.
  2. ↑ "Definition of PROGNOSIS". Merrian-Webster Dictionary. Retrieved October 28, 2018.
  3. ↑ 3.0 3.1 Cairns, R.; Hotopf, M. (January 2005). "A systematic review describing the prognosis of chronic fatigue syndrome". Occupational Medicine (Oxford, England). 55 (1): 20–31. doi:10.1093/occmed/kqi013. ISSN 0962-7480. PMID 15699087.
  4. ↑ 4.0 4.1 Devendorf, Andrew R; Jackson, Carly T; Sunnquist, Madison; Jason, Leonard A (November 28, 2017). "Approaching recovery from myalgic encephalomyelitis and chronic fatigue syndrome: Challenges to consider in research and practice". Journal of Health Psychology. 24 (10): 1412–1424. doi:10.1177/1359105317742195. ISSN 1359-1053. PMC 5930162. PMID 29182007.
  5. ↑ Joyce, J.; Hotopf, M.; Wessely, S. (March 1997). "The prognosis of chronic fatigue and chronic fatigue syndrome: a systematic review". QJM: monthly journal of the Association of Physicians. 90 (3): 223–233. ISSN 1460-2725. PMID 9093600.
  6. ↑ 6.0 6.1 "Prognosis | Presentation and Clinical Course | Healthcare Providers | Myalgic Encephalomyelitis/Chronic Fatigue Syndrome". Centers for Disease Control and Prevention. July 10, 2018. Retrieved October 28, 2018.
  7. ↑ Rowe, Peter C.; Underhill, Rosemary A.; Friedman, Kenneth J.; Gurwitt, Alan; Medow, Marvin S.; Schwartz, Malcolm S.; Speight, Nigel; Stewart, Julian M.; Vallings, Rosamund (2017). "Myalgic Encephalomyelitis/Chronic Fatigue Syndrome Diagnosis and Management in Young People: A Primer". Frontiers in Pediatrics. 5. doi:10.3389/fped.2017.00121. ISSN 2296-2360.
  8. ↑ "What is the prognosis for someone severely affected by M.E.? | 28 July 2017". The ME Association. Retrieved October 27, 2018.
  9. ↑ 9.0 9.1 Peterson, P. K.; Schenck, C.H.; Sherman, R. (May 1991). "Chronic fatigue syndrome in Minnesota". Minnesota Medicine. 74 (5): 21–26. ISSN 0026-556X. PMID 1861659.
  10. ↑ 10.0 10.1 10.2 Wilson, A.; Hickie, I.; Lloyd, A.; Hadzi-Pavlovic, D.; Boughton, C.; Dwyer, J.; Wakefield, D. (March 19, 1994). "Longitudinal study of outcome of chronic fatigue syndrome". BMJ (Clinical research ed.). 308 (6931): 756–759. ISSN 0959-8138. PMC 2539669. PMID 8142830.
  11. ↑ 11.0 11.1 11.2 11.3 11.4 11.5 Vercoulen, J.H.; Swanink, C.M.; Fennis, J.F.; Galama, J.M.; van der Meer, J.W.; Bleijenberg, G. (May 1996). "Prognosis in chronic fatigue syndrome: a prospective study on the natural course". Journal of Neurology, Neurosurgery, and Psychiatry. 60 (5): 489–494. ISSN 0022-3050. PMID 8778251.
  12. ↑ 12.0 12.1 Saltzstein, B. J.; Wyshak, G.; Hubbuch, J.T.; Perry, J.C. (September 1998). "A naturalistic study of the chronic fatigue syndrome among women in primary care". General Hospital Psychiatry. 20 (5): 307–316. ISSN 0163-8343. PMID 9788031.
  13. ↑ 13.0 13.1 13.2 Collin, Simon M.; Crawley, Esther (July 14, 2017). "Specialist treatment of chronic fatigue syndrome/ME: a cohort study among adult patients in England". BMC health services research. 17 (1): 488. doi:10.1186/s12913-017-2437-3. ISSN 1472-6963. PMC 5513420. PMID 28709432.
  14. ↑ Johnston, Samantha; Brenu, Ekua; Staines, Donald; Marshall-Gradisnik, Sonya (2013). "The adoption of chronic fatigue syndrome/myalgic encephalomyelitis case definitions to assess prevalence: a systematic review" (PDF). griffith.edu.au. Annals of Epidemiology. p. 3. doi:10.1016/j.annepidem.2013.04.003. The Australian definition released in 1990 [2],included the same requirements for fatigue, accompanied by neuropsychiatric symptoms such as short term memory loss and difficulties concentrating.
  15. ↑ 15.0 15.1 15.2 15.3 Jason, Leonard A. (February 2011). "Natural History of Chronic Fatigue Syndrome". Rehabilitation psychology. 56 (1): 32–42. doi:10.1037/a0022595. ISSN 0090-5550. PMC 3171164. PMID 21401284.
  16. ↑ 16.0 16.1 16.2 16.3 16.4 16.5 Hill, Nancy F.; Tiersky, Lana A.; Scavalla, Vanessa R.; Lavietes, Marc; Natelson, Benjamin H. (September 1999). "Natural history of severe chronic fatigue syndrome". Archives of Physical Medicine and Rehabilitation. 80 (9): 1090–1094. ISSN 0003-9993. PMID 10489014.
  17. ↑ 17.0 17.1 17.2 17.3 17.4 17.5 Tiersky, Lana A.; DeLuca, J.; Hill, Nancy; Dhar, S.K.; Johnson, S.K.; Lange, Gudrun; Rappolt, G.; Natelson, Benjamin H. (2001). "Longitudinal assessment of neuropsychological functioning, psychiatric status, functional disability and employment status in chronic fatigue syndrome". Applied Neuropsychology. 8 (1): 41–50. doi:10.1207/S15324826AN0801_6. ISSN 0908-4282. PMID 11388123.
  18. ↑ 18.0 18.1 18.2 18.3 18.4 18.5 Andersen, M.M.; Permin, H.; Albrecht, F. (February 2004). "Illness and disability in Danish Chronic Fatigue Syndrome patients at diagnosis and 5-year follow-up". Journal of Psychosomatic Research. 56 (2): 217–229. doi:10.1016/S0022-3999(03)00065-5. ISSN 0022-3999. PMID 15016582.
  19. ↑ Rowe, Peter C.; Marden, Colleen L.; Flaherty, Marissa A.K.; Jasion, Samantha E.; Cranston, Erica M.; Fontaine, Kevin R.; Violand, Richard L. (September 2018). "Two-Year Follow-Up of Impaired Range of Motion in Chronic Fatigue Syndrome". The Journal of Pediatrics. 200: 249–253.e1. doi:10.1016/j.jpeds.2018.05.012. ISSN 1097-6833. PMID 29866593.
  20. ↑ 20.0 20.1 20.2 20.3 20.4 20.5 Reyes, Michele; Dobbins, James G.; Nisenbaum, Rosane; Subedar, Nazerah S.; Randall, Bonnie; Reeves, William C. (January 1999). "Chronic Fatigue Syndrome Progression and Self-Defined Recovery". Journal of Chronic Fatigue Syndrome. 5 (1): 17–27. doi:10.1300/j092v05n01_03. ISSN 1057-3321.
  21. ↑ 21.0 21.1 21.2 21.3 Nisenbaum, Rosane; Jones, James F; Unger, Elizabeth R; Reyes, Michele; Reeves, William C (October 3, 2003). "A population-based study of the clinical course of chronic fatigue syndrome". Health and Quality of Life Outcomes. 1: 49. doi:10.1186/1477-7525-1-49. ISSN 1477-7525. PMID 14613572.
  22. ↑ Tirelli, U.; Marotta, G.; Improta, S.; Pinto, A. (December 1994). "Immunological abnormalities in patients with chronic fatigue syndrome". Scandinavian Journal of Immunology. 40 (6): 601–608. ISSN 0300-9475. PMID 7997849.
  23. ↑ 23.0 23.1 23.2 23.3 Bombardier, C.H.; Buchwald, D. (October 23, 1995). "Outcome and prognosis of patients with chronic fatigue vs chronic fatigue syndrome". Archives of Internal Medicine. 155 (19): 2105–2110. ISSN 0003-9926. PMID 7575071.
  24. ↑ 24.0 24.1 24.2 24.3 24.4 Ray, C.; Jefferies, S.; Weir, W.R. (October 1997). "Coping and other predictors of outcome in chronic fatigue syndrome: a 1-year follow-up". Journal of Psychosomatic Research. 43 (4): 405–415. ISSN 0022-3999. PMID 9330240.
  25. ↑ 25.0 25.1 25.2 25.3 25.4 25.5 Pheley, A.M.; Melby, D.; Schenck, C.; Mandel, J.; Peterson, P.K. (November 1999). "Can we predict recovery in chronic fatigue syndrome?". Minnesota Medicine. 82 (11): 52–56. ISSN 0026-556X. PMID 10589213.
  26. ↑ 26.0 26.1 van der Werf, Sieberen P.; de Vree, Berna; Alberts, Maurice; van der Meer, Jos W.M.; Bleijenberg, Gijs; Netherlands Fatigue Research Group Nijmegen (September 2002). "Natural course and predicting self-reported improvement in patients with chronic fatigue syndrome with a relatively short illness duration". Journal of Psychosomatic Research. 53 (3): 749–753. ISSN 0022-3999. PMID 12217448.
  27. ↑ 27.0 27.1 27.2 27.3 Ciccone, Donald S.; Chandler, Helena K.; Natelson, Benjamin H. (July 2010). "Illness trajectories in the chronic fatigue syndrome: a longitudinal study of improvers versus non-improvers". The Journal of Nervous and Mental Disease. 198 (7): 486–493. doi:10.1097/NMD.0b013e3181e4ce0b. ISSN 1539-736X. PMID 20611051.
  28. ↑ 28.0 28.1 28.2 28.3 28.4 28.5 Nyland, Morten; Naess, Halvor; Birkeland, Jon Steinar; Nyland, Harald (November 1, 2014). "Longitudinal follow-up of employment status in patients with chronic fatigue syndrome after mononucleosis". BMJ Open. 4 (11): e005798. doi:10.1136/bmjopen-2014-005798. ISSN 2044-6055. PMID 25428629.
  29. ↑ 29.0 29.1 Seltzer J. (2018, 29 July). CDC revises its information on ME
  30. ↑ ME Action. September 2018. Recommended Changes to the CDC Webpages on ME.
  31. ↑ Levine, P. H.; Jacobson, S.; Pocinki, A.G.; Cheney, P.; Peterson, D.; Connelly, R.R.; Weil, R.; Robinson, S.M.; Ablashi, D.V. (August 1992). "Clinical, epidemiologic, and virologic studies in four clusters of the chronic fatigue syndrome". Archives of Internal Medicine. 152 (8): 1611–1616. ISSN 0003-9926. PMID 1323246.
  32. ↑ Strickland, Paula S.; Levine, Paul H.; Peterson, Daniel L.; O'Brien, Karen; Fears, Thomas (January 2001). "Neuromyasthenia and Chronic Fatigue Syndrome (CFS) in Northern Nevada/California". Journal of Chronic Fatigue Syndrome. 9 (3–4): 3–14. doi:10.1300/j092v09n03_02. ISSN 1057-3321.
  33. ↑ Levine, P. H.; Snow, P.G.; Ranum, B.A.; Paul, C.; Holmes, M. J. (April 14, 1997). "Epidemic neuromyasthenia and chronic fatigue syndrome in west Otago, New Zealand. A 10-year follow-up". Archives of Internal Medicine. 157 (7): 750–754. ISSN 0003-9926. PMID 9125006.
  34. ↑ Sigurdsson, B. (May 26, 1956). "Clinical findings six years after outbreak of Akureyri disease". Lancet (London, England). 270 (6926): 766–767. ISSN 0140-6736. PMID 13320872.
  35. ↑ Hyde, B.; Bergmann, S. (November 19, 1988). "Akureyri disease (myalgic encephalomyelitis), forty years later". Lancet (London, England). 2 (8621): 1191–1192. ISSN 0140-6736. PMID 2903396.
  36. ↑ "Prognosis | Presentation and Clinical Course | Healthcare Providers | Myalgic Encephalomyelitis/Chronic Fatigue Syndrome". Centers for Disease Control and Prevention. July 10, 2018. Retrieved October 27, 2018.
  37. ↑ "Dr Keith Geraghty on Twitter". Twitter. Retrieved October 27, 2018.
  38. ↑ Rowe, Peter C.; Underhill, Rosemary A.; Friedman, Kenneth J.; Gurwitt, Alan; Medow, Marvin S.; Schwartz, Malcolm S.; Speight, Nigel; Stewart, Julian M.; Vallings, Rosamund (2017). "Myalgic Encephalomyelitis/Chronic Fatigue Syndrome Diagnosis and Management in Young People: A Primer". Frontiers in Pediatrics. 5. doi:10.3389/fped.2017.00121. ISSN 2296-2360.
  39. ↑ Gill, Anna C.; Dosen, Ana; Ziegler, John B. (March 2004). "Chronic fatigue syndrome in adolescents: a follow-up study". Archives of Pediatrics & Adolescent Medicine. 158 (3): 225–229. doi:10.1001/archpedi.158.3.225. ISSN 1072-4710. PMID 14993080.
  40. ↑ van Geelen, Stefan M.; Bakker, Rob J.; Kuis, Wietse; van de Putte, Elise M. (September 2010). "Adolescent chronic fatigue syndrome: a follow-up study". Archives of Pediatrics & Adolescent Medicine. 164 (9): 810–814. doi:10.1001/archpediatrics.2010.145. ISSN 1538-3628. PMID 20819962.
  41. ↑ 41.0 41.1 41.2 Bell, D. S.; Jordan, K.; Robinson, M. (May 2001). "Thirteen-year follow-up of children and adolescents with chronic fatigue syndrome". Pediatrics. 107 (5): 994–998. ISSN 1098-4275. PMID 11331676.
  42. ↑ Rangel, L.; Garralda, M.E.; Levin, M.; Roberts, H. (March 2000). "The course of severe chronic fatigue syndrome in childhood". Journal of the Royal Society of Medicine. 93 (3): 129–134. doi:10.1177/014107680009300306. ISSN 0141-0768. PMC 1297949. PMID 10741312.
  43. ↑ Sulheim, Dag; Hurum, Harald; Helland, Ingrid B; Thaulow, Erik; Wyller, Vegard Bruun (March 21, 2012). "Adolescent chronic fatigue syndrome; a follow-up study displays concurrent improvement of circulatory abnormalities and clinical symptoms". Biopsychosocial Medicine. 6: 10. doi:10.1186/1751-0759-6-10. ISSN 1751-0759. PMC 3337799. PMID 22436201.
  44. ↑ Rimes, Katharine A.; Goodman, Robert; Hotopf, Matthew; Wessely, Simon; Meltzer, Howard; Chalder, Trudie (March 2007). "Incidence, prognosis, and risk factors for fatigue and chronic fatigue syndrome in adolescents: a prospective community study". Pediatrics. 119 (3): e603–609. doi:10.1542/peds.2006-2231. ISSN 1098-4275. PMID 17332180.
  45. ↑ Rowe, Katherine (September 23, 2011), What is the Natural History of Chronic Fatigue Syndrome in Young People? |Abstracts from General Session (PDF), Ottawa, Ontario, Canada: IACFS/ME Biennial International Conference
  46. ↑ Committee on the Diagnostic Criteria for Myalgic Encephalomyelitis/Chronic Fatigue Syndrome; Board on the Health of Select Populations; Institute of Medicine (2015). Beyond Myalgic Encephalomyelitis/Chronic Fatigue Syndrome: Redefining an Illness. The National Academies Collection: Reports funded by National Institutes of Health. Washington (DC): National Academies Press (US). ISBN 9780309316897. PMID 25695122.
  47. ↑ 47.0 47.1 "ME/CFS in Children - by David S. Bell, MD | Open Medicine Foundation". Open Medicine Foundation. June 25, 2016. Retrieved August 11, 2018.
  48. ↑ "Pediatric ME/CFS links". Massachusetts ME/CFS & FM Association. Retrieved August 11, 2018.
  49. ↑ Institute of Medicine (US); Committee on the Diagnostic Criteria for Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (2005). "Beyond Myalgic Encephalomyelitis/Chronic Fatigue Syndrome -- Redefining an illness: Report guide for clinicians" (PDF). nap.edu. p. 5. Retrieved August 25, 2021.
  50. ↑ Carruthers, Bruce; Jain, Anil Kumar; De Meirleir, Kenny; Peterson, Daniel; Klimas, Nancy; Lerner, A. Martin; Bested, Alison; Flor-Henry, Pierre; Joshi, Pradip; Powles, A.C. Peter; Sherkey, Jeffrey; van de Sande, Marjorie (2003). "Myalgic Encephalomyelitis/Chronic Fatigue Syndrome: Clinical Working Case Definition, Diagnostic and Treatment Protocols" (PDF). Journal of Chronic Fatigue Syndrome. 11: 7–36. doi:10.1300/J092v11n01_02.
  51. ↑ Carruthers, Bruce M.; van de Sande, Marjorie I.; De Meirleir, Kenny L.; Klimas, Nancy G.; Broderick, Gordon; Mitchell, Terry; Staines, Donald; Powles, A.C. Peter; Speight, Nigel; Vallings, Rosamund; Bateman, Lucinda; Baumgarten-Austrheim, Barbara; Bell, David; Carlo-Stella, Nicoletta; Chia, John; Darragh, Austin; Jo, Daehyun; Lewis, Donald; Light, Alan; Marshall-Gradisnik, Sonya; Mena, Ismael; Mikovits, Judy; Miwa, Kunihisa; Murovska, Modra; Pall, Martin; Stevens, Staci (August 22, 2011). "Myalgic encephalomyelitis: International Consensus Criteria". Journal of Internal Medicine. 270 (4): 327–338. doi:10.1111/j.1365-2796.2011.02428.x. ISSN 0954-6820. PMC 3427890. PMID 21777306.
  52. ↑ 52.0 52.1 Matthews, Rosalind M.; Komaroff, Anthony L. (January 2007). "Changes in Functional Status in Chronic Fatigue Syndrome Over a Decade". Journal of Chronic Fatigue Syndrome. 14 (1): 33–42. doi:10.1300/j092v14n01_04. ISSN 1057-3321.
  53. ↑ Kidd, Elizabeth; Brown, Abigail; McManimen, Stephanie; Jason, Leonard A.; Newton, Julia L.; Strand, Elin Bolle (April 22, 2016). "The Relationship between Age and Illness Duration in Chronic Fatigue Syndrome". Diagnostics (Basel, Switzerland). 6 (2). doi:10.3390/diagnostics6020016. ISSN 2075-4418. PMC 4931411. PMID 27110826.
  54. ↑ Stordeur S, Thiry N, Eyssen M. Chronisch Vermoeidheidssyndroom: diagnose, behandeling en zorgorganisatie. Health Services Research (HSR). Brussel: Federaal Kenniscentrum voor de Gezondheidszorg (KCE); 2008. KCE reports 88A (D/2008/10.273/58).
  55. ↑ Friedberg, F.; Dechene, L.; McKenzie, M. J.; Fontanetta, R. (January 2000). "Symptom patterns in long-duration chronic fatigue syndrome". Journal of Psychosomatic Research. 48 (1): 59–68. ISSN 0022-3999. PMID 10750631.
  56. ↑ Santamarina-Perez, Pilar; Eiroa-Orosa, Francisco Jose; Freniche, Verónica; Moreno-Mayos, Aurea; Alegre, José; Saez, Naia; Jacas, Carlos (July 2011). "Length of illness does not predict cognitive dysfunction in chronic fatigue syndrome". Applied Neuropsychology. 18 (3): 216–222. doi:10.1080/09084282.2011.595448. ISSN 1532-4826. PMID 21846221.
  57. ↑ Hornig, Mady; Montoya, José G.; Klimas, Nancy G.; Levine, Susan; Felsenstein, Donna; Bateman, Lucinda; Peterson, Daniel L.; Gottschalk, C. Gunnar; Schultz, Andrew F. (February 1, 2015). "Distinct plasma immune signatures in ME/CFS are present early in the course of illness". Science Advances. 1 (1): e1400121. doi:10.1126/sciadv.1400121. ISSN 2375-2548.
  58. ↑ Masuda, Akinori; Nakayama, Takashi; Yamanaka, Takao; Koga, Yasuyuki; Tei, Chuwa (October 2002). "The prognosis after multidisciplinary treatment for patients with postinfectious chronic fatigue syndrome and noninfectious chronic fatigue syndrome". Journal of Behavioral Medicine. 25 (5): 487–497. ISSN 0160-7715. PMID 12442563.
  59. ↑ DeLuca, J.; Johnson, S.K.; Ellis, S.P.; Natelson, B.H. (January 1997). "Sudden vs gradual onset of chronic fatigue syndrome differentiates individuals on cognitive and psychiatric measures". Journal of Psychiatric Research. 31 (1): 83–90. ISSN 0022-3956. PMID 9201650.
  60. ↑ Meeus, Mira; Ickmans, Kelly; Struyf, Filip; Kos, Daphne; Lambrecht, Luc; Willekens, Barbara; Cras, Patrick; Nijs, Jo (January 2016). "What is in a name? Comparing diagnostic criteria for chronic fatigue syndrome with or without fibromyalgia". Clinical Rheumatology. 35 (1): 191–203. doi:10.1007/s10067-014-2793-x. ISSN 1434-9949. PMID 25308475.
  61. ↑ Ickmans, Kelly; Meeus, Mira; De Kooning, Margot; Lambrecht, Luc; Nijs, Jo (February 2014). "Recovery of upper limb muscle function in chronic fatigue syndrome with and without fibromyalgia". European Journal of Clinical Investigation. 44 (2): 153–159. doi:10.1111/eci.12201. ISSN 1365-2362. PMID 24313704.
  62. ↑ Bleijenberg, Gijs (October 6, 2003). "Chronic fatigue and chronic fatigue syndrome in the general population". Health and Quality of Life Outcomes. 1: 52. doi:10.1186/1477-7525-1-52. ISSN 1477-7525. PMID 14613570.
  63. ↑ Hamilton, William T.; Gallagher, Arlene M.; Thomas, Janice M.; White, Peter D. (August 2005). "The prognosis of different fatigue diagnostic labels: a longitudinal survey". Family Practice. 22 (4): 383–388. doi:10.1093/fampra/cmi021. ISSN 0263-2136. PMID 15805126.
  64. ↑ Reyes, Michele; Dobbins, James G.; Nisenbaum, Rosane; Subedar, Nazerah S.; Randall, Bonnie; Reeves, William C. (January 1999). "Chronic Fatigue Syndrome Progression and Self-Defined Recovery". Journal of Chronic Fatigue Syndrome. 5 (1): 17–27. doi:10.1300/j092v05n01_03. ISSN 1057-3321.
  65. ↑ Brown, Molly M.; Bell, David S.; Jason, Leonard A.; Christos, Constance; Bell, David E. (September 2012). "Understanding Long-Term Outcomes of Chronic Fatigue Syndrome". Journal of clinical psychology. 68 (9): 1028–1035. doi:10.1002/jclp.21880. ISSN 0021-9762. PMC 3940158. PMID 22753044.
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  67. ↑ Sankey, Alison; Hill, Catherine M.; Brown, Josie; Quinn, Louise; Fletcher, Anna (January 2006). "A follow-up study of chronic fatigue syndrome in children and adolescents: symptom persistence and school absenteeism". Clinical Child Psychology and Psychiatry. 11 (1): 126–138. doi:10.1177/1359104506059133. ISSN 1359-1045. PMID 17087490.
  68. ↑ Adamowicz, Jenna L.; Caikauskaite, Indre; Friedberg, Fred (November 2014). "Defining recovery in chronic fatigue syndrome: a critical review". Quality of Life Research: An International Journal of Quality of Life Aspects of Treatment, Care and Rehabilitation. 23 (9): 2407–2416. doi:10.1007/s11136-014-0705-9. ISSN 1573-2649. PMID 24791749.
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Centers for Disease Control and Prevention (CDC) - The Centers for Disease Control and Prevention is a U.S. government agency dedicated to epidemiology and public health. It operates under the auspices of the Department of Health and Human Services.

See Centers for Disease Control and Prevention.

etiology The cause of origin, especially of a disease.

post-exertional malaise (PEM) - A notable exacerbation of symptoms brought on by small physical or cognitive exertions. PEM may be referred to as a "crash" or "collapse" and can last for days or weeks. Symptoms can include cognitive impairments, muscle pain, trouble remaining upright (orthostatic intolerance), sleep abnormalities, and gastro-intestinal impairments, and others.

See post-exertional malaise.

NICE guidelines Clinical guidelines used in the UK.

See ME/CFS.

systemic exertion intolerance disease (SEID) - A term for ME/CFS that aims to avoid the stigma associated with the term "chronic fatigue syndrome", while emphasizing the defining characteristic of post-exertional malaise (PEM). SEID was defined as part of the diagnostic criteria put together by the Institute of Medicine (IOM) report of 10 February 2015.

See systemic exertion intolerance disease.

See Canadian consensus criteria.

Canadian Consensus Criteria (CCC) - A set of diagnostic criteria used to diagnose ME/CFS, developed by a group of practicing ME/CFS clinicians in 2003. The CCC is often considered to be the most complex criteria, but possibly the most accurate, with the lowest number of patients meeting the criteria. Led to the development of the International Consensus Criteria (ICC) in 2011.

International Consensus Criteria (ICC) - A set of diagnostic criteria, based on the Canadian Consensus Criteria, that argued for the abandonment of the term "chronic fatigue syndrome" and encouraged the sole use of the term "myalgic encephalomyelitis".

See International Consensus Criteria.

Physical or bodily symptoms. May be used to mean bodily symptoms that are not the result of a known physical or biological illness.<ref>{{Cite web | title = Definition of SOMATIC|website=Merrian-Webster Medical Dictionary|access-date=2019-12-19|url=

somatic symptoms Physical or bodily symptoms. May be used to mean bodily symptoms that are not the result of a known physical or biological illness.

somatic symptoms Physical or bodily symptoms. May be used to mean bodily symptoms that are not the result of a known physical or biological illness.

somatic An adjective relating to the physical body or physical symptoms. It is often contrasted with the adjective "psychological", which refers to the human mind or mental symptoms. In biology, "somatic cells" refer to all the cells of the body, except those which form an egg or sperm.

etiology The cause of origin, especially of a disease.

The BMJ (previously the British Medical Journal) is a weekly peer-reviewed medical journal.

BMJ The BMJ (previously the British Medical Journal) is a weekly peer-reviewed medical journal.

somatic symptom disorder A psychiatric term to describe an alleged condition whereby a person's thoughts somehow cause physical symptoms. The actual existence of such a condition is highly controversial, due to a lack of scientific evidence. It is related to other psychiatric terms, such as "psychosomatic", "neurasthenia", and "hysteria". Older terms include "somatization", "somatoform disorder", and "conversion disorder". Such terms refer to a scientifically-unsupported theory that claims that a wide range of physical symptoms can be created by the human mind, a theory which has been criticized as "mind over matter" parapsychology, a pseudoscience.

myalgic encephalomyelitis (M.E.) - A disease often marked by neurological symptoms, but fatigue is sometimes a symptom as well. Some diagnostic criteria distinguish it from chronic fatigue syndrome, while other diagnostic criteria consider it to be a synonym for chronic fatigue syndrome. A defining characteristic of ME is post-exertional malaise (PEM), or post-exertional neuroimmune exhaustion (PENE), which is a notable exacerbation of symptoms brought on by small exertions. PEM can last for days or weeks. Symptoms can include cognitive impairments, muscle pain (myalgia), trouble remaining upright (orthostatic intolerance), sleep abnormalities, and gastro-intestinal impairments, among others. An estimated 25% of those suffering from ME are housebound or bedbound. The World Health Organization (WHO) classifies ME as a neurological disease.

myalgic encephalomyelitis (M.E.) - A disease often marked by neurological symptoms, but fatigue is sometimes a symptom as well. Some diagnostic criteria distinguish it from chronic fatigue syndrome, while other diagnostic criteria consider it to be a synonym for chronic fatigue syndrome. A defining characteristic of ME is post-exertional malaise (PEM), or post-exertional neuroimmune exhaustion (PENE), which is a notable exacerbation of symptoms brought on by small exertions. PEM can last for days or weeks. Symptoms can include cognitive impairments, muscle pain (myalgia), trouble remaining upright (orthostatic intolerance), sleep abnormalities, and gastro-intestinal impairments, among others. An estimated 25% of those suffering from ME are housebound or bedbound. The World Health Organization (WHO) classifies ME as a neurological disease.

biopsychosocial model (BPS) - A school of thought, usually based in psychology, which claims illness and disease to be the result of the intermingling of biological, psychological and social causes. (Learn more: me-pedia.org)

myalgic encephalomyelitis (M.E.) - A disease often marked by neurological symptoms, but fatigue is sometimes a symptom as well. Some diagnostic criteria distinguish it from chronic fatigue syndrome, while other diagnostic criteria consider it to be a synonym for chronic fatigue syndrome. A defining characteristic of ME is post-exertional malaise (PEM), or post-exertional neuroimmune exhaustion (PENE), which is a notable exacerbation of symptoms brought on by small exertions. PEM can last for days or weeks. Symptoms can include cognitive impairments, muscle pain (myalgia), trouble remaining upright (orthostatic intolerance), sleep abnormalities, and gastro-intestinal impairments, among others. An estimated 25% of those suffering from ME are housebound or bedbound. The World Health Organization (WHO) classifies ME as a neurological disease.

National Academy of Medicine (NAM) - An American non-profit, non-governmental organization which provides expert advice to governmental agencies on issues relating to biomedical science, medicine and health. Formerly known as the Institute of Medicine (IOM).

chronic illness any long-term illness, regardless of the severity. Chronic illnesses are typically incurable, requiring long-term management.

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